My spare is a Mission!
When I replaced the Missions on the ground with Michelins, I kept the Mission spare. And it still holds air fine. My thinking is the same as some others, the spare will only be no the ground long enough to get me to town for repair or replacement of the one that went flat.
Same reasoning for my trucks and cars. I have never bought a new tire for a spare for any of them. And there have been very few spares on any of those trucks and cars that ever hit the ground.
If I had a flat I would probably change it myself even though I have Coach-net.